Study On The Influence Of Caving Ratio To Coal And Gas Outburst

Top-coal caving mining is an important mining method. Top-coal caving mining of coal-gas outburst(Referred to as "outburst") still has two poles apart academic views that restrain and increase outburst danger; in "Safety Regulations in Coal Mine ",outburst coal top-coal caving mining is banned and the basis to determine the caving ratio is insufficient. The influence of the different caving ratio to the outburst risk was studied in the long wall top-coal caving mining with mining height constant. To explore the safety、feasibility、problems and prevention countermeasures of top-coal caving mining of outstanding thick coal seam and provide technical theory and basis for its safety mining.On the basis of surveying top-coal caving mining in outburst thick coal seam and its research status, the influence of the outburst is analyzed from two aspects of gas geology and engineering technology. The influence effect of technical parameter of the caving ratio to the outburst is complex, and the influence of the top-coal caving, coal-winning-machine cutting coal and coal drop position to outburst exist differences. The caving ratio is the main sensitive safety parameters, and the other factors such as working face width, high-low coal mining, mining speed are in subordinate status.Based on the summary long wall top coal caving mining process abutmdent pressure distribution general law research results, stress distribution is simulated by FLAC3D software at the first cutting coal, it is obtained that top-coal caving mining surrounding rock stress redistribution at the beginning of the period before the pressure coming to the roof will lead to stress near the wall concentrated that in the front and back of coal layer and working face stress gradient increased. It is different from the trend that the width of pressure relief area and stress concentration area increased and the peak stress concentration factor and working face stress gradient reduced with the mining height and the mining put thickness increasing during the normal stoping process behind the pressure coming to the roof.According to complex dynamic and static mechanics process of the top-coal caving mining, based on the transient dynamic equation of motion and by using the finite element ANSYS10.0transient analysis module, the mechanics characteristics of top coal caving of stress, strain and elastic energy release evolution distribution are analyzed that are during the initial mining stage and normal phase with the mining height of2.5m and caving ratio of1:3. At the same time, the mechanical characteristics effect that the different caving ratio, roof pressure to it are analyzed. It found that the stress near10m changes during the first put coal process and the stress peak of different caving ratio distributed near the6m, and the stress gradient ahead and behind coal wall increases. The first time put coal release elastic energy of the initial mining stage is3.5times than the release elastic energy during the second time. With the caving ratio increasing, the release elastic near the caving range of20m increases. But at the same time of initial mining stage, if the caving ratio is less than1:3, the increase is not obvious, and if the caving ratio is more than1:3, the release elastic increases fast. The first and cycle pressure of top coal seam roof and the elastic energy release during normal stoping period distributed25m and30m,40m in front of the working, and the amount of central working face is more than both the two sides. And with the caving ratio increasing the release increases; the energy release has concentrated during the roof pressure, and the first weight is two times more than pressure of normal stoping, and it is more than cycle pressure; and the coal displacement near the working face during the first weight and periodic pressure increased significantly. The elastic energy release concentrated in the place20m in front of the working during normal stoping, and with the increase of caving ratio in put growth slowing, the increasing of release range have increase trend. But with the pressure relief zone width increasing, the peak stress concentration factor decreases.Based on the theory analysis of elastic-plastic, rheological that the cut is simplified to circular roadway during initial mining stage:it produces pressure relief belt in a certain range of top coal and on both sides coal wall of the cutting eye roadway; when the top coal of small caving ratio is in the impact range of pressure relief of cutting eye roadway, the affect of the top coal to the outburst danger is small; On the other hand, the top coal of big caving ratio is in’the influence range of stress concentration of cutting eye roadway, the outburst dangerous is increased by top coal.In addition, based on coal seam gas content meeting the Langmuir’s equation, the process of gas flow is isothermal and according with Darcy law, the three-dimensional equation of the variation of working face coal abutment pressure and gas seepage with time is established. Using ANSYS10.0thermal analysis module, the evolution and distribution characteristics in time and space of the top coal caving mining face roadway and top-coal caving mining gas flow field during initial mining stage is simulated. It found that the gas emission width of cutting-hole roadway is about3times as mining height, the gas pressure gradient which is produced by the first coal caving is bigger than the one which is produced by the second coal caving during initial mining stage, and the outburst dangerous of the first coal caving is bigger than the second coal caving.According to the comprehensive research of numerical simulation and theoretical analysis and field data statistical analysis, it is found that the influence law of the caving ratio to the coal-gas outburst danger. In the initial mining stage, if the coal seam thickness is10m and the caving ratio is less than1:3, The impact of the caving ratio to the outburst dangerous is not big; but if it is more than this range, the outburst dangerous increased with the caving ratio increasing. The increase of caving ratio can relieve dangerous of stress-leading outstanding during normal stoping stage.Based on the comprehensive prevention and control technology system of the outburst mine two stage "quaternity", the paper preliminary summarized the reasonable roadway layout and mining technology parameters and the other safety mining technology, at the same time,put forward the new demand of forecast of top coal caving mining working face, and has obtained the good effect in the field application.Forecast drilling should be decorated with two rows to respectively control top-coal mining and mining seam, and with the space between10m and15m. On both sides of the cut-hole and in the front of the working face during initial mining stage, the depth of prediction hole should not be less than10m, and the measuring hole should be6-8m in normal stoping period. Leave10m safety pillar when putting coal and leave5m safety pillar when coal mining during initial mining stage, the prediction advance distance and the measures advance distance arre increased than the average coalface.